1. Field of the Invention
The present invention relates to a skew adjusting apparatus which is used for and is suitable for a remote unit that operates a server placed on a remote place with a keyboard, a mouse, and so on while a user is watching a display, as well as a transmitting and receiving system, and a skew adjusting method.
2. Description of the Related Art
Conventionally, there has been known a remote unit in which a remote server is connected to a display, a keyboard, and a mouse which are provided in the vicinity of a user via a LAN (local Area Network) cable, and the server is operated with the keyboard and the mouse while information is displayed on the display.
In the server side, a transmitting device which transmits signals from the server to the side of the display, the keyboard, and the mouse is provided as a piece of the remote unit, and in the side of the display, the keyboard, and the mouse, a receiving device which receives the signals transmitted from the transmitting device is provided as a piece of the remote unit.
To display an image on the display, the transmitting device transmits three types of RGB video signals to the receiving device with a plurality of signal lines which are connected between the transmitting device and the receiving device. However, when the signal lines connected between the transmitting device and the receiving device have lengths of several hundred meters and more, the lengths of signal lines transmitting a red signal, a green signal, and a blue signal, respectively, are different from each other, and hence differences between arrival times of the respective signals occur. A gap between the phases of the signals causes the color blur and the decrease in definition of characters displayed on the display. Therefore, a skew adjusting apparatus which adjust the differences between the arrival times of the respective signals is provided on the receiving device, so that skews between the signals are adjusted (see Japanese Laid-Open Patent Publication No. 10-13398).
FIG. 1 shows the configuration of a conventional skew adjusting apparatus provided on the receiving device. The receiving device in FIG. 1 is connected to the transmitting device with a LAN cable, and receives the RGB video signals, a horizontal synchronizing signal (Hsync), and a vertical synchronizing signal (Vsync) transmitted from the transmitting device via the LAN cable. Moreover, the receiving device transmits an operation signal input from the keyboard or the mouse to the transmitting device.
In the receiving device, a RGB receiver 201, a delay line 202, and an amplifier 203 are provided for each of RGB signal lines. The skews of the video signals received with the RGB receiver 201 are adjusted with delay elements of the delay line 202. The adjusted video signals are amplified with the amplifier 203, and then are output to the display.
In the receiving device, peak hold circuits 204, 205 and 206, comparators 207, 208 and 209, delay difference-integral circuits 210, 211, 212 and 213, AD (analog-to-digital) converter 214, and a CPU 220 are provided.
The peak hold circuits 204, 205 and 206 are connected to the respective RGB signal lines, and detect the peak values of the RGB signals. The detected peak values are AD-converted with the AD converter 214, and the AD-converted peak values are input to the CPU 220.
The comparators 207, 208 and 209 are also connected to the RGB signal lines, respectively. A reference voltage is input to the comparators 207, 208 and 209. When voltage levels of the RGB signal lines exceed the reference voltage, the comparator 207 outputs a notification signal to the delay difference-integral circuits 210 and 211, the comparator 208 outputs the notification signal to the delay difference-integral circuits 212 and 213, and the comparator 209 outputs the notification signal to the delay difference-integral circuits 210 to 213.
The delay difference-integral circuits 210 to 213 calculate delay-time differences between the blue signal as a reference signal and the red signal or the green signal, by integral. That is, the delay difference-integral circuits 210 calculates the advance-time (R-B) of the red signal from the blue signal as the reference signal, the delay difference-integral circuits 211 calculates the delay-time (B-R) of the red signal from the blue signal as the reference signal, the delay difference-integral circuits 212 calculates the advance-time (G-B) of the green signal from the blue signal as the reference signal, and the delay difference-integral circuits 213 calculates the delay-time (B-G) of the green signal from the blue signal as the reference signal. The pieces of the time information (i.e., the delay-time and the advance-time) calculated with the delay difference-integral circuits 210 to 213 are AD-converted with the AD converter 214, and are output to the CPU 220.
The CPU 220 controls the delay elements provided on the respective RGB signal lines based on the delay-time or the advance-time calculated with the delay difference-integral circuits 210 to 213, and performs skew adjustment between the red signal, the green signal and the blue signal.
However, the conventional skew adjusting apparatus in FIG. 1 uses the delay difference-integral circuits and the AD converter to measure the skews. Therefore, the circuit configuration of the conventional skew adjusting apparatus becomes complex and the cost of the conventional skew adjusting apparatus becomes expensive. Since the delay difference-integral circuits output analog signals, a program of the CPU which adjusts the difference between the phases of the RGB signals based on the measured skews becomes complex.